I agree, including… breathe controller.
My (WIP) 6OP-DX module also embeds 8 CV inputs (any CV may be routed to once/multiple synth parameters).
About generic common breath controller, in general it sends a MIDI CC. So by using MIDI CC→CV module, it will be easy to assign the concerned CV (aka the breathe controller, BTW) to any synth parameters of your choice (except parameters handled by a momentary button, and MASTER level, they’re not CV assignable).
Perhaps it will better - if required - to continue our exchanges in private, or in the 6OP-DX development blog, because this place is dedicated to Voxglitch Community Feedback, in order to respect Bret (and his fantastic stuff).